It's probably the weightiest question in the gym world. What's more effective? Lifting light weight and doing high reps or lifting heavy weight and doing low reps? Body builders and power lifters aside, there seems to be an all too common dividing line between men and women when it comes to weight training. Women are typically worried about "bulking up," and men commonly think that benching as heavy as they can (and sometimes more) is the only way to build up the size of their pecs.

Well, a culmination of new and not-so-new research may blow this conventional wisdom out of the water and right onto the list of "exercise myths," (along with the one about how eating after 8pm makes you fat, and how doing cardio in the low intensity "fat burning" zone burns more fat than higher intensity cardio). Anyone who frequents a gym has probably heard more than one person say that doing short sets of very heavy weight builds big muscles, and doing longer sets of light weight just "tones" muscles. Sounds logical. But several published studies suggest that this is actually not true, and that contrary to popular belief, it doesn't really matter whether you go heavy or light, you'll pretty much get similar results either way if you're trying to build muscular strength -- as long as you lift until you are fatigued or to muscle failure.

Studies have been done on a variety of test subjects ranging from young men to elderly women. The common thread is that whether they went on a strength training program using relatively heavy weights for a small amount of repetitions or a program using relatively light weights for lots of reps, the end results were pretty similar - they all increased muscular strength. When I say "relative," I mean relative to the maximum weight that person can lift for a given exercise. Surprisingly, one recent study done on young men even concluded that "low-load high volume resistance exercise is more effective in inducing acute muscle anabolism than high-load low volume or work matched resistance exercise modes." In simpler terms, this study shows that training with lights weights (just 30 percent of the maximum weight they can lift), is just as or more effective as training with heavy weights (90 percent or their max) to stimulate the synthesis of muscle proteins. Exercise physiologist, author and coach Dr. Jason Karp says that "can translate into muscle growth and strength, as long as each set of training is performed until your muscles fatigue."

Ladies, it's time to put your fears aside. According to all this research, pumping iron won't turn you into the hulk! You can thank genetics for that. Women don't have enough muscle-building testosterone to cause that kind of bulk. Dr. Karp says, "If women want more definition, they should lift heavier since they cannot get bigger muscles because of low testosterone levels. So lifting heavier has the potential to make women more defined." However, in my years of teaching and training, I still get women complaining that their muscles bulk up with even the lightest amount of weights. Again, this is more due to genetics than the amount of weight they're using. No matter how much Pilates and Bar Method you do, you can't actually create "long lean muscles." Dr. Karp chimes in, saying, "'Lean' implies little fat, so for women to get long, lean muscles, they'd have to get rid of the fat that lies above the muscles. Genetics and fiber type plays a huge role in how women will adapt to exercise and ultimately what they will look like." That would answer the question about why some people, men or women, seem to build muscle so easily and others pump their brains out and see very little change in size.

Men, I see this as potentially good news for you! Too many men injure themselves trying to lift as heavy as possible when, according this research, they can lift a little lighter and do more reps while trying to build up the sexy pecs and biceps they're looking for. This could possibly even reduce their risk of injury.

Whether you opt for heavy short sets or lighter longer sets, there is a catch. For muscles to build and strengthen, you do need to lift enough weight and do enough repetitions for the muscle to fatigue or go to failure in 90 seconds or less because you have to be working anaerobically for the proper muscle fibers to be activated. If you're doing biceps curls for a minute and a half and not feeling some serious muscle burn, it's simply too light. Most training experts recommend lifting weights that are somewhere between 60 to 80 percent of the heaviest weight you can lift one time (1RM). For older women, this may be lower. The point is you need to fatigue the muscle you are targeting. I always tell my students and clients that if they don't fatigue the muscle, that muscle won't get the message that it has to get stronger.